138 T
. Moens, M. Vincx J. Exp. Mar. Biol. Ecol. 243 2000 137 –154
extremes on a daily rather than seasonal basis, may be of higher significance in niche differentiation between both species. Their fundamental niche further appears to be determined by
the range of near optimal food conditions, which is narrow in P . marina but comparatively
broader in D . meyli.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Nematodes; Respiration; Feeding; Temperature; Salinity; Food density
1. Introduction
The high species diversity of many meiofaunal communities has long intrigued researchers in marine and estuarine benthic ecology. Nematodes are usually the
dominant metazoan meiofauna in terms of density. Even the most conservative estimates of marine and brackish-water diversity account for several thousand species worldwide;
on a community scale, their diversity is yet more pronounced Fenchel, 1993. In our current understanding, this high species diversity is, however, translated into but a
limited functional diversity. Nematodes may feed on detritus, graze microalgae and bacteria, or forage on protozoan or metazoan prey. Their trophic or functional ecology
has been linked to these major food classes through feeding type classifications, recognizing a mere four to six different trophotypes, with a strong relation between
buccal morphology and feeding ecology Wieser, 1953; Jensen, 1987; Moens and Vincx, 1997. As a consequence, nearly every benthic sample contains many ‘confunctional’
species, which may compete for the same food source, unless they segregate along different microniches. Interspecific differences in the functional response to changes in
food quality and quantity or to a fluctuating abiotic environment may structure these nematode communities Schiemer, 1985, 1987.
A high feeding selectivity among food sources within the trophotypes mentioned above has been demonstrated Tietjen et al., 1970; Tietjen and Lee, 1973, 1977, and
may involve intricate nematode–food interactions, including ‘gardening’ of specific microbiota Riemann and Schrage, 1978; Warwick, 1981a, and a differential taxis
towards specific food spots Moens et al., 1999a. Growth, fecundity Vranken et al., 1988, and taxis Moens et al., 1999a can be strongly affected by food density. Next to
feeding selectivity and food density, adaptations to, or tolerances of, different abiotic conditions may be an important factor structuring aquatic nematode communities
Wieser et al., 1974; Wieser and Schiemer, 1977; Heip et al., 1985.
The difficulty of establishing marine nematode cultures is a major cause for the paucity of information on their physiological, ecological and behavioral responses to
changes in the biotic and abiotic environment. A limited number of species, mainly belonging to the orders Monhysterida and Rhabditida, can, however, be fairly easily
cultured in the laboratory Moens and Vincx, 1998. Both comprise a number of species which are typical of organically enriched habitats in the case of the Rhabditida, only
few species are found in marine or brackish water, and which are often abundant on macrophyte detritus, the decay of which they may considerably enhance Johannes,
1965; Schiemer, 1975; Tenore et al., 1977; Abrams and Mitchell, 1980; Tietjen, 1980;
T . Moens, M. Vincx J. Exp. Mar. Biol. Ecol. 243 2000 137 –154
139
Findlay and Tenore, 1982; Alkemade et al., 1992a,b. Data on ecological and physiological responses of marine and estuarine Monhysteridae and Rhabditida to
changes in food or abiotic conditions include studies of growth and fecundity as a function of temperature 11 species, of salinity five species, of food quality and of
food density two species see Heip et al., 1985, 1995; Vranken, 1985; Vranken et al., 1988, for reviews. These studies include P
. marina as the sole marine rhabditid nematode, and several species of Monhysteridae. Although respiration has been
investigated in some marine nematodes, the respiratory response to temperature and salinity has been established for but a single monhysterid species Warwick, 1981b. No
studies have linked marine or estuarine monhysterid or rhabditid feeding rates to food density.
This paper focuses on one rhabditid and one monhysterid nematode species from an estuarine, intertidal ‘Aufwuchs’ community. It tries to define biotic food supply and
abiotic temperature, salinity ranges and optima a as a means of clarifying zones and periods of occurrence and abundance of these nematodes, and b to get an indication of
the relative importance of food and abiotic variables in determining the community structure in these highly unstable environments.
2. Materials and methods
